A virtual tape system includes a tape library and a virtual tape device. The tape library includes a physical volume (hereinafter referred to as PV) such as a magnetic tape for storing data. The virtual tape device includes a tape volume cache (TVC) and is arranged between a host and the tape library. The TVC is achieved by redundant arrays of inexpensive disks (RAID).
The virtual tape device stores data read from the PV included in the tape library on the TVC as a logical volume (hereinafter referred to as LV). In this manner, the virtual tape system stores the data of the LV on the TVC and reduces operations to be executed for a process of mounting the PV by the tape library and a process of un-mounting the PV by the tape library so as to reduce a time for access to data.
When the virtual tape device receives access to the LV from the host and the LV does not exist on the TVC, the virtual tape device executes a recall process of storing the LV offloaded from the TVC on the TVC. In this case, when the disk cache is full of data, the virtual tape device ensures a region in which a target LV is newly loaded on the disk cache.
For example, the virtual tape device sequentially offloads LVs from the TVC in order from an LV accessed at the earliest time among LVs stored on the TVC, and thereby generates an available region in the disk cache. Then, the virtual tape device allocates the generated available region to an LV that will be newly stored on the TVC.
The aforementioned conventional technique, however, has a problem that a time for the recall process may be long.
When an LV is to be recalled and a PV that stores the LV to be recalled is not mounted in a physical tape drive included in the tape library, the virtual tape device mounts, in the physical tape drive, the PV storing the LV to be recalled.
In order to mount the PV in the physical tape drive, the following process is executed by an operation of a robot in the tape library. First, the robot rewinds a currently mounted PV and unmounts the PV. Subsequently, the robot extracts the PV storing the LV to be recalled from a storage slot and mounts the extracted PV in any of physical tape drives. Then, the robot moves a tape head to a position at which the LV to be recalled has been written.
When a plurality of LVs to be recalled exist and are stored in different PVs, respectively, the robot operation that is the same as the aforementioned process is repeated in the tape library.
Japanese Laid-open Patent Publication No. 2011-123834 is an example of related art.